Follicular thyroid cancer: minimally invasive tumours can give rise to metastases

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Abstract
The histological characteristics of follicular thyroid carcinomas (FTCs) are important predictors of prognosis, and lesions can be classified as either minimally invasive follicular carcinoma (MIFC) or widely invasive follicular carcinoma (WIFC) based on histopathological characteristics. There has been controversy surrounding the histological classification of FTC, which can present challenges to clinicians attempting to deliver accurate prognostic information to their patients. The aim of the present study was to examine cases of metastatic FTC for characteristics that may predict aggressive tumour behaviour. The Monash University Endocrine Surgery Unit database was searched for patients with FTC. The histopathology reports were collated for these patients to confirm the diagnosis of FTC, classify patients into MIFC versus WIFC, and examine for key characteristics such as the capsular and/or vascular invasion. The thyroid specimens from patients with metastatic FTC were examined by reviewing pathologists. It was hypothesized that patients with metastatic disease would likely have WIFC as their primary lesion. There were 64 patients with FTC identified during the period of 1997-2009. Of these, 10 patients were found to have metastatic disease. On review of the histopathology, three patients were found to have WIFC,four patients had MIFC and three patients did not have definite features of FTC found in the thyroid gland. Currently accepted histological classification of FTC is inadequate and fails to accurately predict patients with distant metastatic disease and a more aggressive clinical course. It is thus the policy of our unit to recommend total thyroidectomy and radioactive iodine ablation for all patients with FTC.

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